Backup of a SQL Server may fail with a VSS error.
From the log, the following message can be found:
One or more errors occurred. ---> Replay.Core.Contracts.Transfer.VssGeneralErrorException: There was a problem with the VSS subsystem on '(agent-machine)l'. ---> Replay.Agent.Contracts.ShadowCopy.ShadowCopyWriterFailedException: The VSS writer 'SqlServerWriter' failed during the 'DoSnapshotSet' phase with error WriterErrorNonRetryable. The VSS writer state is FailedAtPrepareSnapshot ---> Replay.Common.Contracts.ReplayException
In the Application event log on the machine, event 8229 is logged:
The problem is most likely due to insufficient access for the SQL Server VSS writer to write to the VSS shadow copy, because the service is not running as an Administrator account, but rather as the Local System account.
From the Rapid Recovery console, take a new snapshot. The backup should now complete without errors.